1. Field of the Invention
This invention relates to a headlamp control circuit that controls a drive of lighting headlamps on a vehicle.
2. Description of the Related Art
Known headlamp systems for a vehicle typically have four-lamps or two-lamps. The four-lamp system has a high-beam headlamp and a low-beam headlamp on each of the right and left sides of a vehicle. The two-lamp system has a high-beam filament and a low-beam filament on each of the right and left sides of the vehicle.
Only the right and left low-beam headlamps of the four-lamp system are lit to make a low-beam condition. However, all four lamps of the four-lamp system are lit to make a high-beam condition.
The right and left low-beam filaments of the two-lamp system are lit to make a low-beam condition, and all four filaments of the two-lamp system also are lit to make a high-beam condition.
A headlamp control circuit that controls a drive of lighting the headlamps includes a switching element to drive the lighting of each headlamp in the four-lamp system and each filament in the two-lamp system. Either system typically includes four switching elements.
JP 2000-233679A discloses a four-lamp system with a single switching element to drive the lighting of right and left high-beam headlamps to downsize a headlamp control circuit or to lower a calorific value. The single switching element disclosed in JP 2000-233679 A for driving the lighting of right and left high-beam headlamps in the four-lamp system results in the right and left low-beam headlamps being lit even if the switching element fails under a high-beam condition. Thus, all headlamps are not brought into a lights-out condition, and security is maintained.
However, if a single switching element drives the lighting of right and left high-beam headlamps in the two-lamp system, there has been a trouble that all headlamps are brought into a lights-out condition if the switching element fails under a high-beam condition.
In view of the above, an object of the invention is to provide a headlamp control circuit for a two-lamp headlight system with a single switching element to drive the lighting of right and left high-beam filaments with a reduced possibility of a lights-out condition if the switching element fails under a high-beam condition.